III. An Organic, Conducive, Habitable MultiUniVerse

I. ExoEarths Everywhere: A Cosmic Census

This image is an artist's depiction of a scalar array of planets in the Milky Way galaxy as detected so far by the NASA Kepler space telescope. It was made to accompany a January 2013 paper by Francois Fressin of the Harvard-Smithsonian Center for Astrophysics presented at a meeting of the American Astronomical Society where he reported that based on the number of Kepler planet finds, our Milky Way galaxy with an estimated 100 billion solar systems could potentially harbor some 17 billion planetary worlds.

As a starter, for web reference sites you can Google: NASA Kepler Satellite, Harvard-Smithsonian Center for Astrophysics, and other centers, along with Exoplanet encyclopedias, some listed here, for a wealth of information. By virtue of space and Earth telescope searches, braced by instrumental and computational analysis, in the past years a grand new cosmos has been revealed that is filled with as many orbital planets as there are sunny stars. A universal, innate propensity to form and evolve solar systems and exoworlds of every possible variety now seems prolifically evident. Circa 2012, it was predicted that bio-friendly Earth analogs in galactic and stellar habitable zones will soon be found.

While this worldwide mission continues apace, by later 2017 it seems that a common occurrence of sapient intelligences and civilizations is becoming much more contingent and tenuous, which is especially documented in Greatest Earth. However, we can now report an expansive and extensive new phase of an exoplanetology field o study every aspect of myriad worlds such as surface to core geochemistry, elemental metallicity, continental mantles, liquid and gaseous atmospheres, moons, host star systems for mobile smaller rocky, Super-Earths, mini-Neptunes to gas giants and so on. These copious studies then intend to access degrees of habitability for microbial to complex life forms. So we coin the phrase A Cosmic Census for these heavenly neighborhood frontiers.

2016 Exoplanet Biosignatures Workshop Without Walls. https://nexss.info/groups/ebwww.
As a habitable cosmos with myriad fertile planets becomes newly evident, a meeting held in June in Seattle under NASA auspices, see below, considered how sapient Earthlings might begin to explore and quantify. It resulted in five papers on the above site, also posted on arXiv. With a lead Exoplanet Biosignature title they are: A Review of Remotely Detectable Signs of Life (1705.05791, Abstract below), Understanding Oxygen as a Biosignature in the Context of Its Environment (1705.07560), A Framework for Their Assessment, (1705.06381), Observational Prospects (1705.07098), and Future Directions (1705.08071). Each has over a dozen authors, which makes up a directory of leading researchers. A future issue of Astrobiology intends to publish.

The Nexus for Exoplanet System Science (NExSS) is a NASA research coordination network dedicated to the study of planetary habitability. The goals of NExSS are to investigate the diversity of exoplanets and to learn how their history, geology, and climate interact to create the conditions for life. NExSS investigators also strive to put planets into an architectural context -- as solar systems built over the eons through dynamical processes and sculpted by stars. Based on our understanding of our own solar system and habitable planet Earth, researchers in the network aim to identify where habitable niches are most likely to occur, which planets are most likely to be habitable. Leveraging current NASA investments in research and missions, NExSS will accelerate the discovery and characterization of other potentially life-bearing worlds in the galaxy, using a systems science approach.

In the coming years and decades, advanced space- and ground-based observatories will allow an unprecedented opportunity to probe the atmospheres and surfaces of potentially habitable exoplanets for signatures of life. Life on Earth, through its gaseous products and reflectance and scattering properties, has imprinted evidence of its presence upon the spectrum of our planet. Aided by the universality of the laws of physics and chemistry, we turn to Earths biosphere, both in the present and through geologic time, for informative analogies of what signatures to search for elsewhere. Here we have compiled an overview of our current understanding of potential exoplanet biosignatures including gaseous, surface, and temporal biosignatures. We additionally survey biogenic spectral features that are well-known in the specialist literature but have not yet been robustly vetted in the context of exoplanet biosignatures. We briefly review advances in assessing biosignature plausibility, including novel methods for determining chemical disequilibrium from remotely obtainable data and assessment tools for determining the minimum biomass required for a given atmospheric signature. (Meeting Abstract)

32 New Exoplanets Found. http://www.eso.org/public/outreach/press-rel/pr-2009/pr-39-09.html.
An October 19, 2009 news release by the European Southern Observatory that its High Accuracy Radial Velocity Planet Searcher satellite has lately been able to detect over thirty additional super-Earth or Neptune-like extrasolar planets. These results were reported at the “Towards Other Earths” conference of the same date held in Porto, Portugal, whose own website is http://www.astro.up.pt/investigacao/conferencias/toe2009/. Commentators mused that a fertile natural nursery is being realized, which seems to want to seed itself with habitable, earth-like ovular worlds.

At Least One in Six Stars Has an Earth-sized Planet. www.cfa.harvard.edu/news/2013/pr201301.html.
A press release by the Harvard Smithsonian Center for Astrophysics about a presentation at the January 2013 meeting of the American Astronomical Society by resident researcher Francois Fressin. His paper proposed that based on awesome results from the Kepler Planet Finder satellite whence almost every star has a solar system, with one/sixth estimated to have an earth analog, then of the 100 billion stars composing our Milky Way there ought to be some 17 billion earth-like worlds amongst our galaxy alone. Of course this went viral in the media, for one example the cover of Macleans Magazine for January 28, 2013 called it “The Greatest Discovery Ever,” which if you really think about its implications is not overstated. An article in the issue “Planet Hunting” by Kate Lunau offers a good review. Fressin’s report will appear in The Astrophysical Journal.

Binary Star Systems. www.space.com/22509-binary-stars.
An informational posting by this science and astronomy site about the prevalence, classes, and evolution of multiple stellar systems. See also Binary Stars on the Australia Telescope National Facility for more info. A consensus is that two or more stars clustered together is a more common astral condition than our single home sun.

Exoplanet Data Explorer. www.exoplanet.org.
A 2017 eclectic repository for all manner of technical findings about vast varieties of astro-globular objects and their relative solar system locales.

The Exoplanet Data Explorer is an interactive table and plotter for exploring and displaying data from the Exoplanet Orbit Database. The Exoplanet Orbit Database is a carefully constructed compilation of quality, spectroscopic orbital parameters of exoplanets orbiting normal stars from the peer-reviewed literature, and updates the Catalog of nearby exoplanets.

Extrasolar Planets Encyclopedia. http://exoplanet.eu/.
A comprehensive site hosted since 1995 by the “Exoplanet team” at the CNRS-LUTH Paris Observatory. When I first logged in this interactive catalog in October 2008, some 300 planets were listed. This number has grown to over 1,800 by April 2014. Many sources and links allow one to visit, e.g. a Habitable Zone Gallery. A technical and popular bibliography is included along with listings of many ground and space research projects.

From Cosmic Births to Living Earths. www.hdstvision.org/report.
A 2015 clarion document from AURA: Association of Universities for Research in Astronomy, Julianne Dalcanton, University of Washington and Sara Seager, MIT, Co-Chairs, for the Future of UVOIR (near ultraviolet to far infrared) Space Astronomy. On this site for a next generation HDST: high definition space telescope beyond Hubble and NASA projects is the main 177 page report, an executive summary, and a press release. The title is a response to a 1997 statement by the Nobel laureate Riccardo Giaconi that the 21st century should have of goal of connecting the development of genetic life to physical universe origins.

The story of life begins with the dark matter seeds of galaxies, which draw together gas from the diffuse cosmic reservoir created in the Big Bang. Galaxies form the stellar nurseries that make stars, without which the cosmos would forever lack the heavy elements and radiation that form and feed life. Stars with a broad spectrum of masses play multiple roles: low-mass stars provide an abundant source of energy for life, while the intermediate and massive stars create and disperse the heavy elements that form life’s raw ingredients. Finally, those heavy elements find their way back into clouds that condense to form low-mass stars and their planets, on which the seeds of life can flourish. (45)

Figure 4-4: The path from Cosmic Birth to Living Earth, witnessed at a range of physical scales, Stars in the first galaxies produce the first heavy elements, which leave those galaxies and recycle into the larger galaxies they become, Mature galactic disks form later, composed of many star-forming regions at 50–100 parsec in size, Inside these regions form multiple star clusters, each of which includes massive stars that forge more heavy elements and low-mass stars that host protoplanetary disks, At 4 - 5 billion years ago, one such disk in our Milky Way formed the Earth and its siblings in the Solar System. (50)

Open Exoplanet Catalogue. www.openexoplanetcatalogue.com.
A home page for a database source of discovered extrasolar planets, almost 3,500 to date. An initial guide lists all exoplanets, habitable zone planets, and planets in binary systems. The site then directs to repositories of detailed specifications.

Vision and Voyages for Planetary Science in the Decade 2013-2022. http://www.nap.edu/catalog.php?record_id=13117.
A 400 page report by the Committee on Planetary Science, Space Studies Board, National Research Council, also published in paper by the National Academies Press (2012). Numerous authorities contribute chapters spanning the formation, variety, material make up, habitability, and so on, of worlds, moons, and stellar systems as we begin to engage this revolutionary vista. With this basis and motive, satellite and exploratory missions are scoped out as earthkinder goes forward in search of new neighbors.

Planetary science is shorthand for the broad array of scientific disciplines that collectively seek answers to basic questions such as how do planets form, how do they work, and why is at least one planet the abode of life. Though deceptively simple, they have spawned a 50-year epic series of exploratory voyages by robotic spacecraft that have visited almost every type of planetary body in humankind’s celestial neighborhood. These robotic voyages have been complemented by investigations with ground- and space-based telescopes, laboratory studies, theoretical studies, and modeling activities. The resulting grand adventure has transformed humankind’s understanding of the collection of objects orbiting the Sun. Mission after mission, study after study, have uncovered stunning new discoveries. Since New Frontiers was published in 2003, ground and space-based planetary science activities have been particularly productive. Some notable examples of recent advances are: • An explosion in the number of known exoplanets; • The Moon is less dry than once thought; • Minerals that must have formed in a diverse set of aqueous environments throughout Martian history; • Extensive deposits of near-surface ice on Mars; • An active meteorological cycle involving liquid methane on Titan. (S-2)

The deep-rooted motives underlying the planetary sciences address issues of profound importance that have been pondered by scientists and non-scientists alike for centuries. They cannot be fully addressed by a single spacecraft mission or series of telescopic observations. Rather they will likely not be completely addressed in this decade or the next. To make progress in organizing and outlining the current state of knowledge, the committee translates and codifies the basic motivations for planetary science into three broad, crosscutting themes: • Building new worlds—understanding solar system beginnings, • Planetary habitats—searching for the requirements for life, and • Workings of solar systems—revealing planetary processes through time. (S-3)

Adibekyan, Vardan.
Formation and Evolution of Exoplanets in Different Environments. arXiv:1701.01661.
We cite this contribution by the University of Porto, Portugal astronomer as a example of how a worldwise Earthkinder is proceeding to study and learn about galactic condensations of a prolific cosmos as it engenders an infinity of orbital worlds. See also Observational Evidence for Two Distinct Giant Planet Populations (1705.06090), and Big, Bigger, Biggest in The Economist for July 15.

The ultimate goal of exoplanetologists is to discover life outside our Earth and to fully understand our place in the Universe. Even though we have never been closer to attaining this goal, we still need to understand how and where the planets (efficiently) form. In this manuscript I briefly discuss the important role of stellar metallicity and chemistry on the formation and evolution of exoplanets.

Adibekyan, Vardan, et al.
How Alien can Alien Worlds Be?. arXiv:1710.07482.
As exoplanetary studies shift from an initial detection stage to an extensive telescopic, instrumental, and computational phase, Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, Portugal researchers provide another review of how this latest project might proceed with regard to what kind of exoworld geochemistry, metallicity, atmospheres, conductivity for life, and more.

In an attempt to select stars that can host planets with characteristics similar to our own, we selected seven solar-type stars known to host planets in the habitable zone and for which spectroscopic stellar parameters are available. For these stars we estimated 'empirical' abundances of O, C, Mg and Si, which in turn we used to derive the iron and water mass fraction of the planet building blocks. Our results show that if rocky planets orbit these stars they might have significantly different compositions between themselves and different from that of our Earth. However, for a meaningful comparison between the compositional properties of exoplanets in the habitable zone and our own planet, a far more sophisticated analysis of a large number of systems with precise mass and radius of planets, and accurate chemical abundances of the host stars. The work presented here is merely the first humble step in this direction. (Abstract)

During (at least) the 11.2 billion year-long history of exoplanet formation in the Milky Way, the interstellar gas has chemically evolved significantly. Some recent works detail how abundances of different chemical elements changes with time and place in the Galaxy. Abundances of these different individual heavy elements and specific elemental ratios (e.g. Mg/Si and Fe/Si) are, in turn, very important for the formation, orbital architecture, structure and composition and even maybe for ’habitability’ of the exoplanets. This discussion leads to a conclusion that the chemical environment i.e., time and place in the Milky Way, play a crucial role for the formation of planets and their main characteristics. (1)

Adibekyan, Vardan, et al.
Which Type of Planets do We Expect to Observe in the Habitable Zone?Origins of Life and Evolution of Biospheres.
Online June,
2016.
With Pedro Figueira and Nuno Santos, University of Porto, Portugal, astrophysicists proceed to quantify our myriad new neighbors so as to identify and characterize what manner are likely to be in conducive locales as our home Earth. See also by the lead author Formation and Evolution of Exoplanets in Different Environments at arXiv:1701.01661. And how fantastic is it that a collaborative planetary species can begin a cosmic census across a widest stochastic diversity of potentially ovular worlds.

We used a sample of super-Earth-like planets detected by the Doppler spectroscopy and transit techniques to explore the dependence of orbital parameters of the planets on the metallicity of their host stars. We confirm the previous results (although still based on small samples of planets) that super-Earths orbiting around metal-rich stars are not observed to be as distant from their host stars as we observe their metal-poor counterparts to be. The orbits of these super-Earths with metal-rich hosts usually do not reach into the Habitable Zone (HZ), keeping them very hot and inhabitable. We found that most of the known planets in the HZ are orbiting their GK-type hosts which are metal-poor. The metal-poor nature of planets in the HZ suggests a high Mg abundance relative to Si and high Si abundance relative to Fe. These results lead us to speculate that HZ planets might be more frequent in the ancient Galaxy and had compositions different from that of our Earth. (Abstract)

The discussion presented above, on the dependence of composition of planets on the chemical properties of their hosts, leads us to speculate that probably the frequency of planets in the HZ was higher in the ancient Galaxy and in the outer disk of the Galaxy, when/where the metallicity is on average lower than in the solar neighborhood. Moreover, most of these planets in the HZ (because of lower metallicity, high Si/Fe, and high Mg/Si) should have composition that might be very different than that of our Earth. (7)